Software engineering courses enable practical learning through assignments requiring contributions to open source software (OSS), allowing students to experience real-world projects, collaborate with global communities, and develop skills and competencies required to succeed in the tech industry. Learning software engineering through open source contribution integrates theory with hands-on practice, as students tackle real challenges in collaborative environments. However, students often struggle to contribute to OSS projects and do not understand the contribution process. Research has demonstrated that strategically incorporating game elements can promote student learning and engagement. This paper proposes and evaluates OSSDoorway, a tool designed to guide students contributing to OSS projects. We recruited 29 students and administered a self-efficacy questionnaire before and after their use of OSSDoorway, along with qualitative feedback to assess challenges, interface features, and suggestions for improvement. The results show that OSSDoorway boosts students' self-efficacy and provides a structured, gamified learning experience. Clear instructions, real-time feedback, and the quest-based system helped students navigate tasks like using GitHub features to submit pull requests and collaborating with the community. Our findings suggest that providing students with a supportive gamified environment that uses feedback and structured quests can help them navigate the OSS contribution process.